In broad terms all VTVM's are alike in concept and differ mainly in build quality and parts tolerance. The calibration instructions for the HP should be close enough to figure out which pot affects which function. Considering the age of the meter you should consider replacing any carbon-comp resistors or tubular condensers that have drifted off the reservation before you calibrate.

DO NOT replace any of the precision 1% resistors in the voltage divider (rotary range switch) unless absolutely necessary as they will be oddball values. Usually they age gracefully, but in a pinch you might cobble together a series / parallel combo of standard value parts close enough to be within range of the tweaker(s).

Thanks, AC5UP. I have the HP 410C manual, but although the two meters are functionally equivalent they are completely different inside. Sort of like the Hallicrafters and Hammarlund versions of the R274 receiver. The build quality of the Hickok is amazing. There are no carbon resistors or paper capacitors. The rotary switches are ceramic. I'm going to have to identify the adjusting pots on the top board in order to dial it in.Roger KF4ZQM

If it were mine I'd eyeball the HP schematic for tell-tales like the wiper of the DC balance pot goes to Pin 4 of V-1. If there's a pot in the Hickok that does the same there's a good chance it's the DC balance adjustment. ( ? )

I usually use the process of elimination as my first strategy when freelancing a repair or restore, divide & conquer comes next. If you can ID four out of the six pots that's better than none. Trial & error is my last option, and there are times when I get there faster than expected...

Replace all the resistors with 1% metal film. It will be a hell of a lot more stable and accurate.

Please, a big lordy NO, in this case.

"There are no carbon resistors or paper capacitors."

The Hickok's were designed and built like the proverbial tanks.

If it is in need of cal and after that procedure is figured out, if it goes back into cal without resorting to an unreasonable trimmer setting, like all the way on the pin or something, no need to troubleshoot anything and by all means no need to blanket replace parts in this one.

However, due to the rigors of time, a very wee spritz of Deoxit on just the contacts on those wafer switches is a very good idea. And if you still need to calibrate, another wee bit on the cal pot and mechanically turn it from pin to pin a few times and then set it to cal point.

I've seen several where the only thing needed was the Deoxit on the contacts and they fell back into cal so close as to make me stop right there.

Tearing down junque in the garage this week and one of the pieces was a Tektronix 500 Series "Type W" o'scope plug-in. Build date of 1967. The plug-in features a DC voltage reference for comparison against an unknown that utilizes a plethora of RCL 1% precision resistors on a rotary switch. Each piece is black plastic, about the size of a pencil eraser, and marked " 1k, .125 watt ".

Just for giggles I checked them with an HP 3466A DMM (a 4.5 digit jobbie that can beat the deep snot out of any Extech for absolute accuracy) and within the lot of 12 pieces they all came up between 1,000.1 and 1,000.3 Ohms.

Oh. My. God.

It's one thing to be on the money, but at that age with that level of consistency?

I am impressed.

BTW: This afternoon I was tearing down an old Harris biz band radio and caught some clever engineering... Visualize the rear heatsink assembly with the usual G-10 Fiberglas PC board and such, and inside the shield over the stripline output section is a pin jack and 1.2k 1/10 watt resistor in parallel with a diode like a 1N4454 hi-speed switch. Totally cool sampling / demod test point built as simply as possible.

Just when you think you can relax, it's suddenly quiz time for Vinnie:

You're tearing down an old Harris business band radio and unplug two small plastic modules. Four pins on the bottom, staggered alignment, they are both identical and have a metal label marked as follows:

Just when you think you can relax, it's suddenly quiz time for Vinnie:

You're tearing down an old Harris business band radio and unplug two small plastic modules. Four pins on the bottom, staggered alignment, they are both identical and have a metal label marked as follows:

VIBRASPONDER (R)Model No. K1000BFreq 100.0 HzMOTOROLA

What is it? What does it do? What's inside? Why a duck?

Have never heard of them. And you should have asked me this afternoon. Still working Saturdays at HRO, and it was slow as crap today. Boring. I was dying to find something to do.

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